In the personal computing industry, multimedia applications are one of the fastest growing areas of technology that exploit the communication medium of personal computers. Personal computers utilize multimedia platforms or boards 11, such as that shown in the conventional multi-media system of FIG. 1, to mix audio inputs from sources such as compact disc drive 13, digital audio tape drive 15, and auxiliary tape drive 17, and to couple the inputs to a common output, such as speaker 19 or a storage medium. In most cases, the input signals are produced by external equipment which are not controlled by the PC and no control exists concerning signal information content, timing, bandwidth, and resolution. The multimedia platform provides a system and method for individually controlling and mixing all input sources to obtain a desired output.
One of the problems with current multimedia boards is that the quality of the output signal is reduced by analog-to-digital and digital-to-analog conversions of data. The conversions are necessitated by the utilization of hybrid analog-digital circuitry. In such conventional systems as shown in FIG. 1, audio signals from various sources are input to a personal computer in digital form. Prior to mixing, the signals are converted into analog form through digital-to-analog converters (D.A.C.) 21 and the amplitudes of the analog signals are adjusted with analog volume controllers 23. The volume-adjusted, analog signals are mixed by analog mixer 24. Thereafter, the mixed signals may be re-digitized by analog-to-digital converters 25 for digitized transmission externally as to a memory device or may be transmitted within the PC in a conventional format compatible with ISA (Industry Standard Architecture) bus 27 or any other conventional bus architecture and protocol, to a destination. At the destination, the digitized mixed signals may be converted to mixed analog signals through D.A.C. 29, volume adjusted by master volume controller 31, and output as mixed sound waves through speaker 19. Thus, conventional systems, such as shown in FIG. 1, require at least two stages of signal conversion. Those stages include a stage transforming the input signals from digital-to-analog format prior to analog mixing and another stage transforming the mixed signals from analog-to-digital format.
In conventional systems as shown in FIG. 1, processing and storing audio signals introduces noise and distortions into the original wave forms of the audio input signals. For example, audio input signals may be distorted by analog-to-digital conversion prior to storage or digital-to-analog conversion prior to playback. Each such data conversion and corresponding data format change may cause as much as 10 dB degradation in the output signal quality. Thus, the overall quality of the final mixed audio is diminished by the interchange of signal formats.
In addition, volume control, analog mixing, and filtering devices reduce system performance as the devices age or are altered by temperature fluctuations. These effects inject large amounts of noise into analog sub-systems. Further, analog signals may be parsed through band-limiting filters to reduce the amount of memory necessary to store the signals. However, these band-limiting filter techniques provide poor stopband characteristics and their transition bands are not very sharp. Accordingly, there is a need for a multimedia platform that accepts multiple audio input signals, digitally adjusts and mixes the audio input signals, and digitally outputs merged audio signals.